1. Field of the Invention
The present invention relates to a method of manufacturing a capacitor of a semiconductor device, and more particularly to a method of manufacturing a capacitor having high capacitance using a (Ta2O5)1xe2x88x92xxe2x80x94(TiO2)x thin film as the dielectric layer.
2. Description of the Related Art
It is well known that a capacitor may function as a storage device for storing data in a memory device such as a DRAM (Dynamic Random Access Memory). Such a capacitor typically has a dielectric layer which is interposed between a lower electrode and an upper electrode. The capacitance of the resulting capacitor is proportional to the surface area of the electrode and the dielectric constant of the dielectric layer and is inversely proportional to the spacing between the electrodes, i.e., the thickness of the dielectric layer. Consequently, the capacitance of the capacitor may be increased by increasing the surface area of the electrode, using the dielectric layer having a higher dielectric constant, and/or decreasing the thickness of the dielectric layer.
However, there is a limit to decreasing the thickness of the dielectric layer without inducing unacceptable numbers of dielectric failures. And, methods of increasing the surface area of the electrode tend to complicate the manufacture process of the lower electrode or have detrimental effects on the stability of subsequent processes. Therefore, the current efforts to manufacture capacitors having high capacitance are mainly focused on methods of developing a dielectric layer having a high dielectric constant.
As an example, a conventional capacitor uses a NO thin film having a nitride/oxide structure as a dielectric layer. Because the dielectric constant xcex5 of the NO thin film is typically about 4xcx9c5, it is difficult to manufacture a capacitor having sufficiently high capacitance using a NO thin film without making other compromises. Therefore, a Ta2O5 thin film was considered as an alternate dielectric layer material instead of the NO thin film. A Ta2O5 thin film has a substantially higher dielectric constant, typically about 25xcx9c27. Therefore, a capacitor using a Ta2O5 thin film as a dielectric layer can easily be applied to the next generation DRAM products of more than 256M which require high capacitance of more than 25 fF/cell. The process according to the present invention also has the added advantage of suppressing the generation of soft errors while reducing the refresh time.
However, it is difficult to use the Ta2O5 thin film as a dielectric layer for of several reasons. First, the Ta2O5 thin film has unstable stoichiometry, an exchangeable Ta atom in an oxygen vacancy state allows some leakage current to be generated in in the film. Accordingly, after depositing the Ta2O5 thin film, both a rapid thermal process and a multi-step low temperature oxidizing process for removing the oxygen vacancy are typically performed, thereby complicating the formation of the Ta2O5 thin film.
Second, the Ta2O5 thin film has a high oxidation reaction to both polysilicon and TiN, two materials commonly used to form the lower electrode and an upper electrode. As a result, oxygen from the Ta2O5 film tends to react with the electrodes during subsequent thermal processes, thereby forming a low dielectric oxide layer on each interface. Accordingly, the electrical characteristics of a Ta2O5 capacitor are degraded as a result of the formation of these the low dielectric oxide layers.
Third, organic matter from the tantalum (V) ethoxide Ta(OC2H5)5, a precursor of Ta2O5, reacts with O2 or N2O gas, carbon, carbon compounds such as CH4 and C2H, and moisture(H2O) which are incorporated into and exist as impurities in the Ta2O5 thin film. The presence of these impurities increases the leakage current and degrades the capacitor""s dielectric characteristics.
Accordingly, it is the object of the present invention to provide a method of manufacturing a capacitor for a semiconductor device capable of solving the problems caused by the oxygen vacancies and impurities to obtain high capacitance and low leakage by utilizing a (Ta2O5)1xe2x88x92x-(TiO2)x thin film as a dielectric layer.
To accomplish the aforementioned object, a method of manufacturing a capacitor of a semiconductor device according to the present invention comprises the steps of: providing a semiconductor substrate over which selected lower patterns are formed and an intermediate insulating layer is covered; forming a lower electrode on the intermediate insulating layer; depositing a (Ta2O5)1xe2x88x92xxe2x80x94(TiO2) thin film in an amorphous state on the lower electrode; annealing the amorphous (Ta2O5)1xe2x88x92xxe2x80x94(TiO2)x thin film at a low temperature; annealing the low temperature annealed amorphous (Ta2O5)1xe2x88x92xxe2x80x94(TiO2)x thin film at a high temperature so as to form a crystalline (Ta2O5)1xe2x88x92x-(TiO2)x thin film as a dielectric layer; and forming an upper electrode on the (Ta2O5)1xe2x88x92xxe2x80x94(TiO2)x thin film.